I. Introduction: Peach leaf curl is a fungus disease that, under the right conditions, can cause severe
early defoliation and crop loss on nearly all peach and nectarine cultivars. Because of
weather factors and good grower management practices in most years, however, the disease
often causes little or no significant damage or loss. For this reason, the destructive
potential of leaf curl is frequently underestimated to the point where important control
measures may be forgotten or delayed.
II. Symptoms: As the name of the disease implies,
the most common and striking symptom of leaf curl occurs on the foliage. Infected leaves
are severely deformed and often display a variety of colors ranging from light green and
yellow to shades of red and purple. The fungus causes the meristematic cells at leaf
margins to proliferate quickly and randomly, which results in the leaves becoming
variously wrinkled, puckered, and curled (photo 2-54). As these infected leaves mature,
naked asci containing ascospores of the pathogen are produced on the surface giving them a
dusty appearance, after which the leaves turn brown, shrivel, and drop from the tree. Many
infected fruits drop early and go unnoticed; those that remain may become crooked at the
stem end like a small yellow squash, while others develop reddish to purple, wart-like
deformities on the fruit surface (photo 2-55).
III. Disease Cycle: The pathogen occurs commonly
almost wherever peaches are grown, and overwinters as blastospores in protected crevices
in the bark and around the buds. Primary infections are the most damaging and occur during
the early spring from bud swell, when the bud scales loosen, until the first young leaves
are fully emerged from the bud. Infections on young peach leaves occur at temperatures of
50 to 70 F (10-21 C). Little infection occurs below 45 F (7 C). The incidence of infection
is greatest when rains wash the overwintered spores into the bud and cool temperatures
lengthen the time that the emerging leaves are exposed to the pathogen, before they are
fully expanded and can resist penetration by the fungus. When temperatures following bud
swell are warm and early leaf development is rapid, infections rarely become established,
even when spring rains occur.
Monitoring: Treatments for leaf curl are not effective after infections occur or after
symptoms appear. Monitoring during bloom is done largely for the purpose of assessing the
effectiveness of the control program and planning for next season. Monitor young leaves on
sample trees for early foliar symptoms (photo 2-54) and record the incidence of leaf curl
on sample trees.
V. Management: In most areas of the
eastern U.S., leaf curl can be controlled with one well-timed fungicide application,
either in the autumn after 90% of the leaves have fallen, or in the spring before bud
swell. All cultivars are susceptible to leaf curl to some degree, although Redhaven
and cultivars derived from Redhaven are more resistant to leaf curl than Redskin and
cultivars derived from Redskin. If leaf curl is severe, it is important to maintain
tree vigor by thinning more fruit than normal, reducing drought stress with
irrigation, and applying extra nitrogen fertilizer.
Chemical control -
Chemical control - home
orchardists (pdf file - Acrobat Reader required)
Text prepared by P. W. Steiner and A. R.
Download this file in pdf format (Acrobat Reader required).